This invention relates to apparatus for thermally treating pulverized or pulverulent material such as the raw material which is burned in calcining for the preparation of cement, and more particularly to an apparatus which includes a furnace, such as a rotary kiln for the final complete burning or calcining of the material and which delivers its exhaust gases to parallelly arranged first and second preheating chambers to preheat the material onto a plurality of sets of cyclone separators which utilize exhaust gases for further preheating and precalcining.
As recognized in the above referred to Deussner et al. application, Ser. No. 507,378, now abandoned, devices have heretofore been provided in the prior art for the heating of pulverized material and for the calcining of cement such as shown and described in the published German Patent application No. 1,184,744 for the production of alpha-aluminum oxide from aluminum oxide hydrates.
The aforementioned Deussner et al. application, Ser. No. 507,378, now abandoned, has provided a device for the thermal treatment of earth alkaline carbonates in which there is an effective and efficient thermal treatment for pulverized raw material, and which is particularly suitable for use in the commercial manufacture of cement. According to Deussner et al., a preheating chamber is provided in advance of the main furnace or kiln or calcining chamber. Additional thermal energy is provided in the preheating chamber by a burner which is so positioned that the flow of gases from the furnace feed into the preheating chamber in advance of the inlet of the material feed conduit. Material arrives flowing against the direction of flow of exhaust gases from the furnace. At the area of the inlet point of the burner, a secondary air feed conduit discharges into the preheating chamber. The material is preheated with the hot exhaust gases coming from the furnace, and is partially calcined in this chamber. The preheating calcining zone accomplishes an almost complete irradiation of the CO.sub.2 when the apparatus and method are used in the manufacture of cement, and the structure is used before the introduction of the raw material into a rotary kiln or furnace. With the preheating chamber and the passing of the material through a series of cyclone separators, a substantially complete calcining of the material is obtained before introduction thereof into the rotary kiln. This permits reduction in the size of furnace and the thermal load carried thereby. As a result, only the heat which is required for the sintering process is introduced into the rotary kiln. With this structure, as mentioned above, a partially calcined material which is preheated by means of hot exhaust gases in the preheating device, for example, pulverized raw material used in the manufacture of cement, is fed in a finely dispersed form and distributed uniformly practically over the entire front cross section and into direct contact with the combustion zone so that an almost complete calcining, that is, an also complete expulsion of the CO.sub.2 is attained in the case of pulverized raw material used in the manufacture of cement, before introduction of the material into the rotary kiln.
In the above referred to devices, the deacidification of the cement raw material in the heat exchange system may be almost completely carried out in advance of the rotary furnace so that in the rotary kiln, only the clinker formation, that is, the finished burning needs to be carried out. This results in an appreciable thermal release in the rotary kiln so that an increase in yield without noteworthy increase in dimensions of the device is possible. However, with the preheating mechanisms in advance of the furnace, particularly with large yields, difficulties are encountered in conducting the additional combustion zones optimumly. Difficulties are also encountered with variation in load conditions to attain the desired complete calcination of the charging material before introduction into the furnace.
It is, accordingly, an object of the present invention to improve mechanism such as described so that it will satisfy a wide variation of requirements of operation and may be used and constructed independently of size dimensions.
In accordance with the present invention, the flow of exhaust gases from the furnace is divided into at least two separate paths to be conducted through parallel preheat chambers, each of which is provided with an independent fuel supply. This provides that even with devices for the largest output commercial yields, the flow cross-section in the area of the additional combustion zone in the preheater may be limited. This obtains an optimum utilization of fuel. This further obtains an optimum deacidification of the raw material in the partial stream. In the essentially flameless combustion that occurs due to the reaction of the exhaust gases from the furnace in the separate preheating chambers with the material being fed therein, an essentially disturbance free and almost complete deacidification of material can be attained. Also, by partial load adjustment for the preheat chambers which is enhanced by the limitation of the size of the individual flow cross-sections of the preheat chamber, a homogeneous dispersion of the raw material occurs. This permits operation with a relatively uniform flow of the material into the preheat chamber and of the gases from the furnace through the preheat chamber. For deacidification of fine granular cement raw material, the quantities of fuel introduced react with the quantities of oxygen contained in the furnace exhaust gases or react with additionally introduced heated combustion air during the release of heat. Through the high utilization of heat in the deacidification operation in the preheat chamber, so much heat is utilized that no flame can develop so that with proper distribution as is accomplished with the present arrangement, complete deacidification can be obtained at very high flow volumes generating heat with the introduction of fuel and oxygen without the development of a flame, and yet attaining high heat utilization. Disadvantages of previous structures are prevented which encounter problems due to bad distribution or disturbances caused by caking or banking of the materials, and this can occur if sintering occurs through uneven heat treatment.